Atrial Septal Defect

Aetiology
Ostium secundum defect (75% of cases)- due to excessive resorption of the septum primum or inadequate development of septum secundum
Ostium primum defect: Due to incomplete fusion of the atrioventricular endocardial cushions
Incomplete closure of foramen ovale

Epidemiology

Incidence 6.4/ 10,000 live births

F:M= 2:1

Accounts for 5-10% of congenital heart disease

Second most common congenital heart disease of adults (30-40%)

Pathophysiology
ASD allows left-to-right shunting(acynotic), resulting in volume overload of right atrium & right ventricle, increades pulmonary blood flow, right atrium enlargement, right ventricle, pulmonary artery, ultimately pulmonary hypertension

Reversal of shunting when pulmonary pressure> systemic pressure

Presentation

• systolic ejection murmur at the lower left sternal border
• widely split & fixed S1
• ocassionally, a loud S1 & pulmonary ejection click
• findings vary with the size of the defect
• usually asymptomatic in childhood
• exercise intolerance in older children

DDx

• VSD
• Peripheral pulmonary stenosis
• Aortic stenosis
• PDA
• coarctation of the aorta

Investigation
ECG-

-ostium secundum defects- incomplete right bundle branch block & right axis deviation

-ostium primum defects: Right bundle branch block, left axis deviation, 1st degree atrioventricular block

CXR- pulmonary artery, right atrium, right ventricular enlargement, left atrial enlargement may be present in ostium primum or long-standing ostium secundum defects

Echo+dopler- confirm dx

Cardiac catheter indicated in ASD

-Right heart- determine degree of shunting & pulmonary hypertension

-Left ventricular angiography may show a gooseneck deformity in the outflow tract (subaortic stenosis) in ostium primum defects

MRI- define anatomic location and size of defect

Management

Surgical closure 

• surgical patch, suture-based closure, catheter based closure
• Ostium primum defect closure requires patch closure of the septal defect with mitral valve repair if a cleft mitral leaflet is present
• Contraindications for repair of an ASD include severe pulmonary hypertension or reversal of intracardiac shunt with resting O2 saturation <90%

Elective surgical repair - preschool years- optimal repair prior to age 25 with pulmonary astery systolic pressure <40mmHg

Prognosis

spontaneously close in 1st year of life

Most are symptomatic until adulthood

Residual shunt in 7-8% closure

Catheter closure has 95% success rate mith minimal residual shunting

Operative mortality for uncomplicated secundum defects= 1-3%